Device for producing halftone patterns



Oct. 29, 1963 G. KARGL DEVICE FOR PRoDUcING HALFTONE PATTERNS Filed Oct. 17. 1961 l l x l I I I I l i -1 l 1 GODFRIED KARGL INVENTOR.

Oct 29, 1963 G. KARGL 3,109,059

DEVICE FOR PEoDucING HALFTONE PATTERNS Filed Oct. 17. 1961 3 Sheets-Sheet 2 7 GODFRIED KARGL IN VEN TOR.

AGENT Oct. 29, 1963 G. KARGL DEVICE FOR PRoDucING HALFTONE PATTERNS 5 Sheets-Sheet 5 Filed 0G13. 17. 1961 GATE .5 RECORDING HEAD GODFRIED KARGI.

INVENTOR.

AGENT United States Patent O Ali esslisehaiit, Meidling, Austria, a corporation or Austria Filed @et 17, wel, Ser. Mind? Claims priority, application Austria Set. i7, ldt, Claims.. (Ci. 17g-M3) My present invention relates to a device for making socalled halftone patterns adapted to be used in the photoengraving art for reproducing the various shadings of photographs and other originals with continuous tone gradation.

Several systems are known wherein the resulting printing plate is provided with `a pattern of engraved dots varying in depth and/ or width with the shade to Ibe reproduced so that corresponding tones are obtained by -virtue of the diiferent quantities of ink stored therein. The size of each dot may be inversely or directly proportional to the brightness of a corresponding elemental area of the original so that the reproduction twill be either a positive or a negative replica of the master.

An object of my invention is to provide a device of this character which insures precise correlation betwn a scanning element and a recording tool controlled thereby so as to improve the idelity of reproduction.

A more specific object of this -invention is to provide means in such device for establishing an exact relationship between the scan and the positions of the dots so that, particularly `for multicolor printing7 several patterns can be produced from an original in accurately interleaved relationship.

Another object of the instant invention is to provide rneans for instantly `switching from positive to negative reproduction, or vice versa.

A further object of the invention is to provide means for conveniently varying the scale of reproduction without requiring the original to be photographically reduced or enlarged prior to recording.

-In accordance with this invention l provide a stationary mounting for the original and a movable carriage on which there are supported, in relatively fixed positions, a photoelectric scanner and a recording stylus controlled by the scanner, this stylus co-operating with a iixedly held blank on which the dotted pattern is to be formed. The carriage, in turn, is displaceable at a relatively slow rate in a rst direction and reciprocable `at a relatively fast rate in a second direction preferably orthogonally related to the tirst, the two movements being exactly coordinated so that any traverse in the second direction corresponds to a predetermined increment of advance in the iirst direction; such advance, moreover, occurs intermittently between successive reciprocations so that the path of the carriage remains linear during each traverse and all traverses are precisely parallel to one another.

ln order to correlate the formation of the dots with the two-dimensional scan, the control circuit for the recording tool is intermittently deactivated by an interruptor synchronized with the carriage drive. ln a preferred embodiment, in which the interrupter comprises a rotating light chopper such `as a disk with peripheral perforations periodically translurninated by a suitable light source to actuate a photocell, this ylight chopper is positively coupled with a lead screw driven by a reversible motor whose sense of rotation is changed whenever' the carriage operates a limit switch on arriving in either terminal position of its reciprocating stroke; at the same time, at the instant of reversal, another lead screw is stepped through a fraction of a revolution under the control of the same limit switch to advance the carriage.

Patented @ich 29, 1963 For multicolor reproductions the light-chopper disk may be provided with a plurality of relatively staggered rows of perforations which can be selectively brought into play, concurrently with a corresponding change in the angular position of the intermittently stepped lead screw, whereby the dots of the respective color screens so produced will be relatively oiset in both dimensions.

Still another feature of my invention resides in the mounting of the original on a iixed but preferably adjustable projector Whose focal plane, rather than the original itself, lies in the scanning path of the photoelectric sensor. A particularly compact arrangement utilizes a deilector for directing the light rays from the projector upwardly toward the scanner; the projector is horizontally shiftable for varying the image scale.

The above objects, features and advantages of the present invention Iwill become more fully apparent from the following detailed description, reference being made to the accompanying drawing in which:

FG, l is an overall side view of a device embodying the invention;

Fl'G. 2 is a top View of the device;

FIG. 3 is la sectional view taken on line llilll of FlG. 2;

FiG. 4 is a detail view of of the device;

5 is a cross-section on line V-V of FlG. 2;

FIG. 6 is a circuit diagram of the electrical and electromechanical components of the device;

FIG. 7 is a fragmentary elevational view of a control disk included in the device;

FIG. 8 is a 'diagrammatic representation of part of a gravure plate made with the disk of FlG. 7; and

FIG. 9 is a cross-section of the reproducing head forming part of the device.

An image of an original to be copied is produced in the focal plane 3, onto which it may be focused with the aid or" a ground-glass plate (not shown) temporarily positiontable in that plane on a table 111, by a projector il and a mirror 2. Upon insertion of the original in the projector l, the size of this image is ydetermined by the placement of the projector which can be longitudinally displaced on its bed lill by a knob itl@ `and whose focal length can be varied in the conventional manner. The image is scanned by a photocell l which is iixedly mounted on a carriage 5. The raster or dot structure is produced under the control of the photocell by a stylus 4d on a recording head o which is also mounted on carriage 5 and reproduces the image on a writing surface 7 supported on the stationary table lill. This produces a one-to-onescale reproduction which in turn enables the scale ratio or" the copy relative to the original to be selected freely by a corresponding setting of the projector.

As shown in FlGS. l-3, carriage `5 slides on two rods S and S and is driven therealong by a lead screw il. Screw 9 `and rods 8 and d `are retained in a frame it) which rides on a pair of rixed rails 169, ildl, perpendicular' to the rods 8, d', and receives its motion along these rails from a drive nut `l2 engageable with a second lead screw `lill. Screw il is driven by a motor )i3 `through a transmission ld. v

A color filter lill-l is shown removably inserted in the light path from projector l to image plane 2:.

A second photocell iii?? is also mounted on carriage S and scans a broad area around the spot seen by photocell l to provide a reference signal dependent upon average brightness. Cells d and iti?) are connected to the circuit components in a chassis on carriage '5 by leads lll? `and ltl. Power supply lilo is connected to chassis -lild by a ilexible cable E95.

The elements it, ltl and o, while relatively riXed during each scanning operation, may be independently adpart of the feed mechanism justed on the carriage by suitable means not further illustrated; they may be displaceable especially in a direction para lel to lead screw il.

In order to provide Va reciprocating motion for frame llt', two limit switches lSa, las and .5b, leb are provided beneath the trarne at the end points of its travel. These switches are actuated by a projection i7 on trame l@ and their armatures lea, lob reverse the drive motor l?, so that the frame it@ automatical'ly goes back and forth between the switches. The position `of switches ida, 16a 'and 15b, lob can be manually adjusted by sett screws lilla and ltllb. The system is so arranged that any depression of armature lia or b closes a circuit for advancing the lead Yscrew 9 by a fraction of a turn.

The voltage generated in the picture photocell fr 'is irst applied to `a pre-amplilier 2;7 (FiG. 6). To eliminate errors caused by the sensitivity Ito temperature of the photocell and of any semiconductors used in the pre-ampliiier, l prov-ide a compensating arrangement comprising another photocell 1%, which is initially shielded against an action of light, and another amplifier ZS. This amplifier is so connected to the pre-amplier 2,7 that the picture signal appearing Vat the output of the preamplier corresponds to the diierential voltage between amplifier 27 and amplifier 23. The biasing resistance 28d of one of the amplifiers, in the present case the arnplilier 23, is provided with a tap, adjustable to determine a reference level for the dierential voltage. This enables a selection both or" the magnitude and of the polarity of the diterential voltage. Thus, au increasing brightness of the picture may have an increasing or decreasing picture sigual associated with it and a positive picture can be produced from a negative or positive master. The ampliiier 23 may also be used for scanning the area around the raster dot. It is known that this enables a control of the tonal value. Amplitiers having appropriate characteristic curves will enable the generation of a suitably corrected differential voltage without requiring the usual modulating stage.

This differential voltage is now fed to the gate 2g, which transforms it into the pulses required for the tormation of the raster. The gate 29 is controlled by a photocell (pulse photocell) llt? or Sil' so that the raster pulses are positively dependent on the position of the picture photocell, i.e., also on the mechanism for moving the carriage. This is effected by a perforated disc 3l, which is carried by and xed to the screw il. Through the holes of the perforated disc ,31 the pulse photocell 30 will receive a light impulse from `a lamp 32 whenever a hole passes the cell 3d, which transforms this impulse into a -voltage pulse to which the gate 29 is responsive. This will result in the appearance of a chopped DC. voltage at the output of this switch. The level of this DC. Ivoltage will correspond to the brightness of the light falling on the photocell at a given time. Since the pre-amplifier 27 is not capable of delivering a power output `suliicient for operating the recording head, a power amplifier 33 is provided, which may consist of a normal audio-frequency ampliiier. feeds the recording head 6 through the intermediary of a suitable matching element.

`Switch armatures la, leb control the operation of motor 13 through the intermediary of a relay M5 which, upon being energized by the momentary closure of switch lha in the lett-hand end position of frame l@ (PEG. 3), locks over its armature llSa in series with switch armature 'Mb so that its holdino circuit is subsequently broken by the momentary opening of switch lr6/J in the opposite end position `of the frame. Relay armatures lSb, M are thus alternately attracted and released to reverse the motor current.

The circuit alternately closed by the parallel-connected switches 15a and lSb contains one solenoid liti connected in series with these switches and source 2th?. T he core V19 of this solenoid is linked via spring 7? with a paw-i The power amplifier 2l serving lto step a ratchet 22. The solenoid i8 is carried on the frame 1t? and connected to switches 15a, 15b by ilexi'ole wires. Ratchet 22 is fastened to lead screw 9 which therefore tums with it and produces a line-by-line advance of the carriage 5 along rods S, '8'.

Flin 4 illustrates the structural details of the stepping mechanism associated `with ratchet Z2. lt includes a second ratchet wheel which is ailixed to screw 9 and has `the same number of teeth as wheel 22 facing, however, in the opposite direction. Ratchet {Si} coactswith a pawl 5.2 normally held against a stop 53 by a spring lltlZ. Pawl S2 is cammed inwardly .by a contact finger 5l which is attached -to a lever 2t), whenever solenoid 13 attracts its core 119. Lever 2i), secured to pawl 2l and journaled on screw 9, is swingable between two stops 2da, 24h. lust before lever 2d reaches stop 24b, pawl 52 engages ratchet 5t) yand stops it, and with it ratchet 22 and lead screw 9, the spring 7@ absorbing the magnetic pull of solenoid core 19 as the pawl 21 is prevented from pushing the engaged tooth of ratchet 22 beyond the point at which pawl 52 contacts the flank of the nearest tooth of ratchet 5t). This double-ratchet escapement assures that the lead screw 9 will be rotated through exactly the same ang-le during each step and there will be no overrun caused by inertia.

ln order that the carriage 5 may be quickly returned to its Voriginal position after a scan is completed, :l prefer to couple it to the lead screw 9 not by a conventional drive nut but by a spring 25', as shown in FIG. 5, which engages the thread of this lead screw. The spring Z5 can be disengaged by a button 26 to free the carriage 5; when the'button 26 is released, the spring 25 re-engages the threads of lead screw 9.

VLight sources 32, 32 are respectively aligned with photocells 39, 3d' from which they are separated by an interposed disk Sli rotating with screw lll.. Disk 31 has as many circular rows of perforations as there are photocells and light sources, only two sets of holes 131, 131' being shown in this instance (see also FlG. 8). These sets of holes are angularly staggered by an arc t1=t/ 2, the arc t' representing the `angular division of each row 33E., i3d'. Lt will be understood that additional rows, if provided, would be odset in analogous manner from those illustrated, eg. by t/4 if the total number of rows were four. For simplicitys sake, only one photocell 30 and one lamp 32 have been shown in FIG. 2.

FiG. 7 illustrates, diagrammatically, the patterns of dots 231, 231i obtainable with perforations 1311 and 131', respectively. Dots 231 (solid lines) are produced when the switch 66 occupies the position shown in FIG. 6 to energize photocell Sil; dots 235i correspond to the alternate switch position in which photocell 30 responds. The relative spacing t1 between adjacent dots 231 and 231 equals half the distance t between successive dots 231 or iii-3l in conformity with the staggering of holes 131 and ll. How the vertical interleaving (as viewed in FIG. 7) of the two rows ot dots 2.3i, 231 is accomplished will be explained hereinafter.

For this purpose the stops 24a, 24h and 53 and the springs 23, llt@ and ythe solenoid '1S las well as the pivot of the lever 5'2 Iare carried by a common carrier 210, which is supported by the trarne llt) and pivotally movable about the axis of the screw 9 and can be tiXed in its adjusted position. The carrier has arcuate slots 221 traversed by bolts .'ZllZ` which are held in the frame 10. With the kaid of nuts, not shown, the connection between the parts itt) and 2l@ may be established Iand released. The length of the slot 221 corresponds to the maximum staggering between the dots 231 and the dots 231 in adjacent lines.

Tie actual production of the dot structure or raster is done by the electrodynamic writing head o whose details are shown in Fifi. 9. The electric impulses from the power amplifier 33 are transmitted to the stylus d which ma. es a dot on the blank 7, eg. a sheet of paper,

for each impulse. A moving coil 41 travels in the air gap of a magnetic system formed by several magnets 37, yokes 3S and 39 and core Al). Coil 4f, traversed by the output current of amplifier 33, is seated in a block 42 which is suspended on two parallel leaf springs 43 and d3. The coil is thus guided so that it can move only in a direction parallel to the axis of the core dit. rllie stylus 44 is also afiixed to block d2.

When an impulse :is received from the amplifier 33, the coil 41 is axially displaced and the stylus 4d is pressed onto the writing surface and, by means of a suitably colored iii-k ribbon 45, produces a dot of the raster. The amount of pressure on the writing surface and, therefore, the size of the dot are proportional to the intensity of the impulse received. ln order accurately to control the distance of the swinging arm from the writing surface 7', a foot 46 is provided which can be adjusted by a screw 47; this foot could, of course, also be replaced Aby a roller or the like if desired. In order to establish a maximum size for the dot independently of the intensity of the impulse, foot 46 carries a set screw 48 which limits the travel of the block 42. In order to reduce reverberations on impact, the oscillating system is provided with an elastic stop 49 in a recess of the block d2.

My invention is, of course, not limited to the specific arrangement described and illustrated. Thus it will be apparent, for example, that the stylus t4 may be replaced by any suitable recording tool for marking a receiving surface and that more than one disk, in lieu of the single light chopper 31, may be provided to accommodate the different sets of perforatioins 131i, i331. These and other modifications readily apparent Vto persons skilled in the ant are intended to be embraced in the spirit and scope of the invention as defined in the appended claims.

I claim:

l. A device for producing halftone patterns, comprising a support, first mounting means for fixedly holding an original on said suppont, second mounting means for fixedly holding a recording blank on said support, said original being so position-able on said first mounting means as to be scannable by a motion parallel to the surface of said blank, a carriage displaceable on said support in a first direction and in a substantially perpendicular second direction both parallel to said surface, photoelectric sensing means fixedly mounted on said carriage for scanning said original, recording means positioned on said carriage at a fixed location thereof in proximity to said surface with freedom of relative transverse displacement for marking said blank, first drive means for reciprocating said carriage in said first direction, second drive: means synchronized with said first drive means for intermittently advancing said carriage in said second direction between reoiprocations of said first drive means, transmission means coupling said recording means with said sensing means for controlling the marking of said blank in iaccordaiice with the brightness of the original as scanned by said sensing means, and interrupter means coupled with said first drive means for periodically iriaetivating said transmission means at `a rate which is high relative to the rate of reciprocation of said carriage; said `transmission means including a first and a second amplifier, said sensing means comprising a photoelectric scanning cell connected to control said first amplifier, said second amplifier being connected to a source of reference potential, and an output circuit differentially connected across the outputs of said amplifiers, said first and second amplifiers being included in respective Iarms of a bridge circuit, said output circuit lying in an output diagonal of said bridge circuit.

2. A device for producing halftone patterns, comprising a support, first mounting means for fixedly holding an original on said support, second mounting means for fixedly holding a recording blank on said support, said original being so positionable on said first mounting means as to be scannable by a motion parallel -to the surface of said blank, a carriage displaceable on said support in a first direction and in a substantially perpendicular second direction both parallel to said surface, photoeleotric sensing means fixedly mounted on said carriage for scanning said original, recording means positioned on said carriage at a fixed location thereof in proximity lto said surface with freedom of relative transverse displacement for mark-ing said blank, first drive means for reciprocating said carriage in said first direction, second drive means synchronized with said first drive means for intermittently advancing said carriage -in said second direction between reciprocations of said first drive means, transmission means coupling said recording means with said sensing means for controlling the marking of said blank in accordance with the brightness of :the original las scanned by said sensing means, and interruptor means coupled with said first drive means for periodically inactivating said transmission means at a rate which is high relative yto the rate of reciprocation of said carriage; said carriage being provided with a supporting frame therefor, said first drive means comprising a first lead screw on said support engaging said frame, reversible motor means coupled with said first lead screw and a pair of limit switches actua-table by said frame in respective termi-nal positions thereof for alternately operating said motor means iii opposite directions, thereby reciprocating said frame along with said carriage between said terminal positions, said second drive means comprising a second lead screw on said frame engaging said carriage and stepping means co-ntrolled by said limit switches for rotating said second lead screw through a fraction of a turn in each of said terminal positions.

3. A device according to claim 2 wherein said stepping means comprises a ratchet means on said second lead screw, eleotromagnetically controlled first pawl means engageable with said ratchet means for rotating said second lead screw, and second pawl means coupled with said first pawl means and engageable with said ratchet means for arresting said second lead screw upon rotation through a predetermined angle.

4. A device according to claim 3 wherein said ratchet means comprises a pair of ratchet wheels respectively engageable by said first and second pawl means, said wheels having like numbers of teeth facing in opposite directions. l

5. A device according to claim 3 wherein said stepping means further comprises a solenoid provided with a core, a lever journaled on said second lead screw and linked with said core, said first pawl means being secured to said lever, and cam means rigid with said lever for moving said second pawl means into engagement :with said ratchet means.

6. A device according to claim 2 wherein said interrupter means comprises rotatable light-chopper means on said first lead screw, photocell means on one side of said light-chopper means and a source of light on the other side of said light-chopper means, the latter having perforations for intermittently exposing said photocell means to illumination by said source of light.

7. A device according to claim 6 wherein said lightchopper means comprises at least one disk ywith a plurality of rows of angularly spaced perforations, the perforations of said rows having the same angular spacing but being angularly staggered relatively to one another, said photocell means being selectively illuminable through iany of said rows for varying the phase relationship between said interrupter means and said first drive means.

8. A device according to claim 7, further comprising adjusting means for modifying the operation of said stepping means in a manner changing the phase relationship between said first and second drive means concurrently with selection of a different row of said perforations for illuminating said photocell means.

9. A device according to claim 2 wherein said carriage is provided with a coupling spring normally engaging the threads of said second lead screw and with release means for disengaging said spring from said second lead screw prior to returning said carriage yto a starting position on said frame.

1G. A device according to claim l wherein said second amplifier is provided with sw-itchover means for varying the clective magnitude of said reference potential between ltwo values, thereby reversing the polarity of a voltage differential developed across said output diagonal.

ll. A device according -to claim l, further comprising a photcelectric control cell positioned to receive background illumination from said original, said control cell being connected to said second amplifier for delivering thereto a reference potential proportional to said background illumination.

l2, A device for producing haltone patterns, comprising a support, stationary projector means on said support adapted to produce an image of an original in a predetermined plane, mounting means for tixedly holding a recording blank on said support with its surface parallel to said plane, a carriage displaceable onsaid support in a tirst direction and in a substantially perpendicular second direction both parallel to said plane and said surface, photoelectric sensing means iixedly mounted on said carriage for scanning said image, recording means positioned on said carriage at la fixed location thereof in proximity to said surface with freedom of relative transverse displacement or marking said blank, iirst drive means for reciprocating said carriage in said first direction, second drive means synchronized with said rst drive means for intermittently advancing carriage in said second direction between reciprocations of said irst drive means, transmission means coupling said recording means with said sensing means for controlling the marking of said blank in accordance with the brightness of said image as scanned by said sensing means, and interruptor means coupled with said irst drive means for periodically in activating said transmission means at a rate which is higlny reative to the rate of reciprocation of said carri-age.

13. A device according to claim l2 wherein said projector means is adjustably positioned on said support and ccusable upon said plane with diierent image patios.

14. A device according to claim 13 wherein said support comprises a table with an aperture for the rays of said projector means, said sensing means being kdisplaceabie Vabove said table, said projector means being horizontally shiftable below said table, further comprising reiiecting means beiow said table directing said rays upwardly through said aperture.

15. A device according to claim 14 wherein said table is provided with means for temporarily positioning a ground-glass plate at said aperture.

References Cited in the iile of this patent UNITED STATES PATENTS 500,282 Edison a June 27, 1893 2,965,712 Pike et al Dec. 20, 1960 2,986,598 Hell May 20, 1961 

1. A DEVICE FOR PRODUCING HALFTONE PATTERNS, COMPRISING A SUPPORT, FIRST MOUNTING MEANS FOR FIXEDLY HOLDING AN ORIGINAL ON SAID SUPPORT, SECOND MOUNTING MEANS FOR FIXEDLY HOLDING A RECORDING BLANK ON SAID SUPPORT, SAID ORIGINAL BEING SO POSITIONABLE ON SAID FIRST MOUNTING MEANS AS TO BE SCANNABLE BY A MOTION PARALLEL TO THE SURFACE OF SAID BLANK, A CARRIAGE DISPLACEABLE ON SAID SUPPORT IN A FIRST DIRECTION AND IN A SUBSTANTIALLY PERPENDICULAR SECOND DIRECTION BOTH PARALLEL TO SAID SURFACE, PHOTOELECTRIC SENSING MEANS FIXEDLY MOUNTED ON SAID CARRIAGE FOR SCANNING SAID ORIGINAL, RECORDING MEANS POSITIONED ON SAID CARRIAGE AT A FIXED LOCATION THEREOF IN PROXIMITY TO SAID SURFACE WITH FREEDOM OF RELATIVE TRANSVERSE DISPLACEMENT FOR MARKING SAID BLANK, FIRST DRIVE MEANS FOR RECIPROCATING SAID CARRIAGE IN SAID FIRST DIRECTION, SECOND DRIVE MEANS SYNCHRONIZED WITH SAID FIRST DRIVE MEANS FOR INTERMITTENTLY ADVANCING SAID CARRIAGE IN SAID SECOND DIRECTION BETWEEN RECIPROCATIONS OF SAID FIRST DRIVE MEANS, TRANSMISSION MEANS COUPLING SAID RECORDING MEANS WITH SAID SENSING MEANS FOR CONTROLLING THE MARKING OF SAID BLANK IN ACCORDANCE WITH THE BRIGHTNESS OF THE ORIGINAL AS SCANNED BY SAID SENSING MEANS, AND INTERRUPTER MEANS COUPLED WITH SAID FIRST DRIVE MEANS FOR PERIODICALLY INACTIVATING SAID TRANSMISSION MEANS AT A RATE WHICH IS HIGH RELATIVE TO THE RATE OF RECIPROCATION OF SAID CARRIAGE; SAID TRANSMISSION MEANS INCLUDING A FIRST AND A SECOND AMPLIFIER, SAID SENSING MEANS COMPRISING A PHOTOELECTRIC SCANNING CELL CONNECTED TO CONTROL SAID FIRST AMPLIFIER, SAID SECOND AMPLIFIER BEING CONNECTED TO A SOURCE OF REFERENCE POTENTIAL, AND AN OUTPUT CIRCUIT DIFFERENTIALLY CONNECTED ACROSS THE OUTPUTS OF SAID AMPLIFIERS, SAID FIRST AND SECOND AMPLIFIERS BEING INCLUDED IN RESPECTIVE ARMS OF A BRIDGE CIRCUIT, SAID OUTPUT CIRCUIT LYING IN AN OUTPUT DIAGONAL OF SAID BRIDGE CIRCUIT. 